I've tried 47 AI on the Nordschleife a few times, didn't go too bad. I always started at the back of the grid and there was a couple of traffic jams towards the start from someone loosing it, but if I don't try to win the race in the first couple of miles the traffic thins out and the racing if fine. Haven't tried a multi-lap race to see if there's a chance of catching the leaders. Performance isn't bad either, with 15 AI and starting from the back, I was getting about 68 FPS the then 90-120 for the rest. With 47 AI, again starting from the back, I was getting 55 FPS then 70-110 once things spread out some.
It's always going to be challenging starting with such a large grid, and would need a long race to place up the leaderboard. I had one race where an accident on maybe the 4 or 5 turn allowed me to jump 8-9 places but very easy to get caught up in the accidents if pushing too hard to soon.
Loving this sim, my favorite of all (pCARS, AC, AMS, rF2, Dirt Rally, ...) especially after the latest updates.